linux-kernel - RE: [RFC PATCH 1/2] spi: Add multiple CS support for a single SPI device

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Date:   Wed, 27 Jul 2022 13:02:31 +0000
From:   "Mahapatra, Amit Kumar" <amit.kumar-mahapatra@....com>
To:     Mark Brown <broonie@...nel.org>
CC:     Amit Kumar Mahapatra <amit.kumar-mahapatra@...inx.com>,
        "p.yadav@...com" <p.yadav@...com>,
        "miquel.raynal@...tlin.com" <miquel.raynal@...tlin.com>,
        "richard@....at" <richard@....at>,
        "vigneshr@...com" <vigneshr@...com>,
        "git@...inx.com" <git@...inx.com>,
        "michal.simek@...inx.com" <michal.simek@...inx.com>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "michael@...le.cc" <michael@...le.cc>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "git (AMD-Xilinx)" <git@....com>
Subject: RE: [RFC PATCH 1/2] spi: Add multiple CS support for a single SPI
 device

Hello Mark,

> -----Original Message-----
> From: Mark Brown <broonie@...nel.org>
> Sent: Tuesday, July 19, 2022 11:23 PM
> To: Mahapatra, Amit Kumar <amit.kumar-mahapatra@....com>
> Cc: Amit Kumar Mahapatra <amit.kumar-mahapatra@...inx.com>;
> p.yadav@...com; miquel.raynal@...tlin.com; richard@....at;
> vigneshr@...com; git@...inx.com; michal.simek@...inx.com; linux-
> spi@...r.kernel.org; linux-arm-kernel@...ts.infradead.org; linux-
> kernel@...r.kernel.org; michael@...le.cc; linux-mtd@...ts.infradead.org;
> git (AMD-Xilinx) <git@....com>
> Subject: Re: [RFC PATCH 1/2] spi: Add multiple CS support for a single SPI
> device
> 
> On Tue, Jul 19, 2022 at 01:21:41PM +0000, Mahapatra, Amit Kumar wrote:
> 
> > I agree, so for checking the controller multiple chip select
> > capability(using more than one chip select at once) we can define a
> > new spi controller DT property like "multi-cs-cap"(please suggest a better
> name).
> > The controller that can support multiple chip selects should have this
> > property in the spi controller DT node. The spi core will check
> > ctlr->multi-cs-cap to operate multiple chip select in parallel.
> 
> I'm not sure this needs to be a DT property, it's more just something we infer
> from the compatible.  The name seems fine, as does the flag in the controller
> data.

I agree that we can infer this from the compatible and set the flag in the controller data.

> 
> > > the chip selects are available and that the controller can do
> > > something useful with them (and probably have an implementation in
> > > the core for doing so via GPIO).
> 
> > Here are you referring to the usecase in which a controller
> > implementing multi CS support using GPIO?
> 
> Yes, we probably ought to.

In my next version I will add the implementation in the spi core for multi CS support using GPIO, but I will not be able test it as I don't have the necessary hardware setup .

Regards,
Amit